package com.ozo.news.util;

public class SnowFlake {

    /**

     * 起始的时间戳

     */

    private final static long START_STMP = 1480166465631L;

    /**

     * 每一部分占用的位数

     */

    private final static long SEQUENCE_BIT = 7; //序列号占用的位数

    private final static long MACHINE_BIT = 4;  //机器标识占用的位数

    private final static long DATACENTER_BIT = 4;//数据中心占用的位数

    /**

     * 每一部分的最大值

     */

    private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);

    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);

    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    /**

     * 每一部分向左的位移

     */

    private final static long MACHINE_LEFT = SEQUENCE_BIT;

    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;

    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long datacenterId;  //数据中心

    private long machineId;    //机器标识

    private long sequence = 0L; //序列号

    private long lastStmp = -1L;//上一次时间戳

    public SnowFlake(long datacenterId, long machineId) {

        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {

            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");

        }

        if (machineId > MAX_MACHINE_NUM || machineId < 0) {

            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");

        }

        this.datacenterId = datacenterId;

        this.machineId = machineId;

    }

    /**

     * 产生下一个ID

     *

     * @return

     */

    public synchronized long nextId() {

        long currStmp = getNewstmp();

        if (currStmp < lastStmp) {

            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");

        }

        if (currStmp == lastStmp) {

            //相同毫秒内，序列号自增

            sequence = (sequence + 1) & MAX_SEQUENCE;

            //同一毫秒的序列数已经达到最大

            if (sequence == 0L) {

                currStmp = getNextMill();

            }

        } else {

            //不同毫秒内，序列号置为0

            sequence = 0L;

        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分

                | datacenterId << DATACENTER_LEFT      //数据中心部分

                | machineId << MACHINE_LEFT            //机器标识部分

                | sequence;                            //序列号部分

    }

    private long getNextMill() {

        long mill = getNewstmp();

        while (mill <= lastStmp) {

            mill = getNewstmp();

        }

        return mill;

    }

    private long getNewstmp() {

        return System.currentTimeMillis();

    }

    public static void main(String[] args) {

        SnowFlake snowFlake = new SnowFlake(2, 3);

        for (int i = 0; i < (1 << 12); i++) {

            System.out.println(snowFlake.nextId());

        }

    }

}